Jenkins: make it possible to run notebooks from external repos programmatically

[tlvu]

This is done via the CONFIG_PARAMETERS_SCRIPT_URL override. See the sample jenkins-params-external-repos.include.sh where I run external notebooks from https://github.com/roocs/rook/tree/master/notebooks.

Changes:

• Do not download repos not enabled to run (fixes https://github.com/Ouranosinc/PAVICS-e2e-workflow-tests/issues/30).
• Do not hardcode the list of archiveArtifacts in Jenkinsfile because the list of repos is dynamic now.
• (Breaking) Archived build artifacts of original notebooks moved to under buildout/ dir, together with their corresponding *.output.ipynb files. Previously they were at the same checkout path as their repo.
• downloadrepos is both a script and a library to centralize all helper functions in one place. Otherwise we would have helpers for downloading repos in one file and helpers for other tasks in other files. Backward compatibility is preserved when downloadrepos is used as a script in autodeploy of tutorial notebooks to the Jupyter env.
• NBVAL_SANITIZE_CFG_FILE and DEFAULT_PRODUCTION_HOST now can also be overridden by the external repo if needed.

This PR is almost fixing https://github.com/Ouranosinc/PAVICS-e2e-workflow-tests/issues/57.

There is no easy way to programmatically change the Jenkins "build request UI" to add on-the-fly the new params for the external repo. I think we will have to have another separate Jenkinsfile.other_repo.

This PR would help testing https://github.com/bird-house/birdhouse-deploy/issues/455.

@mishaschwartz This would be useful to you if you have notebooks for your own WPS services.

[fmigneault]

Testing on http://daccs-jenkins.crim.ca/job/DACCS-iac-birdhouse/2649/ Triggered http://daccs-jenkins.crim.ca/job/PAVICS-e2e-workflow-tests/job/make-it-easier-to-add-new-nb-or-repos/3

[tlvu]

Testing on http://daccs-jenkins.crim.ca/job/DACCS-iac-birdhouse/2649/ Triggered http://daccs-jenkins.crim.ca/job/PAVICS-e2e-workflow-tests/job/make-it-easier-to-add-new-nb-or-repos/3

You should try https://daccs-jenkins.crim.ca/job/PAVICS-e2e-workflow-tests/job/make-it-easier-to-add-new-nb-or-repos/build?delay=0sec

and set CONFIG_PARAMETERS_SCRIPT_URL="https://raw.githubusercontent.com/Ouranosinc/PAVICS-e2e-workflow-tests/25c0abb438c43b6d8de313e98684dca5846b0231/test-override/jenkins-params-external-repos.include.sh"